An apparatus for controlling tire inflation pressure of this kind is disclosed, for example, in Japanese. Patent Application Laid-Open (kokai) No. Hei 11-139118 (hereinafter referred to as Patent Document 1). In the apparatus for controlling tire inflation pressure described in the Patent Document 1, the pressurized air supplied from the pressure generating device can be introduced (supplied) into the tire air chamber of the vehicle wheel assembly, and accordingly, the air pressure in the tire air chamber can be secured.
Meanwhile, the apparatus for controlling tire inflation pressure described in the Patent Document 1 is constructed in such a manner that the supplying passageway provided in the axle hub is communicatively connected to the introducing passageway provided in the wheel of the vehicle wheel assembly though an air tube. Therefore, when the vehicle wheel assembly is being mounted onto the flange portion of the axle hub, it is required to relatively adjust a position of the supplying passageway provided in the axle hub to a position of the introducing passageway provided in the wheel of the vehicle wheel assembly, and to communicatively connect the supplying passageway provided in the axle hub to the introducing passageway provided in the wheel of the vehicle wheel assembly through the air tube, leaving room for improvement due to difficulties in mounting.